1. Field of the Invention
The present invention relates to an electromagnetic actuator based on the operation principle of galvanometer operated mirror utilizing the process for manufacturing semiconductor devices, such as transistors or integrated circuits.
2. Brief Description of the Related Art
Examples of electromagnetic actuators of such a type are disclosed in Japanese laid-open publication Nos. 5-320524, 6-9824 6-310657 and 6-327569.
Disclosed in Japanese laid-open publication Nos. 5-320524 is a fundamental model of an electromagnetic actuator of this type, comprising a semiconductor substrate, on which a movable plate and a torsion bar are integrally mounted, wherein the torsion bar swingably suppors the movable plate with respect to the substrate, a driving coil is formed around the movable plate, a galvanometer operated mirror mounted to the movable plate, and means for generating a magnetic field for applying a magnetic field for the driving coil; and the movable plate is driven by the galvano-miller by flowing a current through the driving coil.
Laid-open publication No. 6-9824 discloses substantially the fundamental model as described above, but modified in that a detection coil for positional detection of the movable plate is connected to the driving coil.
Laid-open publication No. 6-310657 discloses an optical detector of the type in which the direction of the optical axis is variable, wherein the mirror in the galvanometer operated mirror disclosed in No. 5-320524 or No. 6-9824 is replaced by a photo-dedector element.
Finally, Laid-open publication No. 6-327369 discloses an electro magnetic actuator of the type, such as galvanometer operated mirror or optical axis variable type, in which a torsion bar is made of electro-conductive to form an electric connection, so as to prevent disconnection of the wiring pattern around the torsion bar caused by the repetion of torsional action of the torsion bar.
The electromagnetic actuator disclosed in Laid-open publication No. 6-310657 is described below as to the embodiment thereof.
RELATED ART 1
With reference to enlarged views of FIGS. 32 and 33, as the related art 1, the arrangement of "an optical detector of the type in which the direction of the optical axis is varable" is described. The examples of the related arts 1 to 3 hereinafter are all of the type which operates by the same principle of the galvanometer. Also, the drawings including FIGS. 34 to 39 are all enlarged views.
In FIGS. 32 and 33, the optical detector 1 of the type in which the direction of the optical axis is varable is composed of a three-layered structure, including a silicone base 2 as a semiconductor substrate, and a pair of borosilicate glass bases 3 and 4 bonded on the upper and lower surfaces of the silicone base.
Here, there is the Joule's loss due to the resistance component in the coil, and sometimes the driving ability is limited due to generated heat, and, therefore, the flat coil 7 is formed by electroforming, comprising the steps of: sputtering a thin nickel layer on a substrate, forming thereon a copper layer by Cu electrolytic plating, and removing part of Cu and Ni layer leaving the coil pattern to form the flat coil, featured in forming the thin layer coil with low resistance and high density, providing the micromagnetic device with miniturlized and thinned profile.
On the upper central area of the coil, a pn photodiode 8 is formed in a known process, and a pair of electrode terminals 9, 9 connect to the flat coil 7 via the portion of torsion bar 6, where the terminals 9, 9 are formed simultaneously with forming of the flat coil 7.
On both sides, referring to FIG. 32, of substrates 3 and 4, each pair-formed annular permanent magnets 10A, 10B; and 11A, 11B apply a magnetic field on the flat coil in the region parallel with the torsion bar axis. Three pairs of magnets 10, 10B, each pair therein being vertically arranged, are located such that the polarity is uniform, e.g., all N-poles locate lower sides, and S-poles upper sides as in FIG. 33. Similarly, the other three pairs 11A, 11B are located so as to have the polarity opposite to the above-mentioned pairs 10A and 10B.
Also, on the lower side of the glass base 4, a pair of coils are patterned and provided, which are connected to the paired terminals 13 and 14 (Schematically depicted by one dotted line in FIG. 32, but actually a plurality of turns). The detection coils 12A, 12B are located synmetrically relative to torsion bar 6, to detect the displacement angle of movable plate 5, and are located so that the mutual inductance between the flat coil 7 and detection coils 12A, 12B varies so as to increase when one of these approaches the other, and decrease when the other is away from the other. For example, by detecting the change of the voltage signal produced due to the mutual inductance, the displacement angle of movable plate 5 can be detected.
In operation, when a current is flowed across one terminal 9 and the other terminal 9 as + and - electodes, respectively, a magnetic field is formed so as to cross the flat coil 7 as the arrows B in FIG. 34 shows. When a current flows via the coil 7, a force F is applied on flat coil 7, or, in other words, across the ends of movable plate 5, in the direction according to the Flemming's left-hand law, and such a force is obtained by the Lorentz' law.
The force F is obtained by the following formula (1), when i is current density flowing across the coil 7, and B is magnetic flux formed by the upper and lower magnets: EQU F=i*B (1)
Actually, depending on the turn number n of coil 7, and the coil length w along which the force F is applied, the force F is again: EQU F=nw(i*B) (2)
On the other hand, by rotation of movable plate 5, the torsion bar 6 is tilted, the relation between the opposed spring force F' and the displacement angle .phi. of movable plate 5 is as follows: EQU .phi.=(Mx/GIp)=(F'L/8.5*109r4)*11 (3)
Where Mx: torsional moment, G: lateral elastic coefficient, Ip: polar sectional secondary moment. L, 11 and r are, respectively, the distance from the central axis to the force point, the length of the torsion bar, and the radius of torsion bar as shown in FIG. 34.
As the movable plate 5 rotates until where the forces F and F' reach to their balanced state, the displacement angle varies in proportional with the current "i".
By controlling the current flowing via the coil 7, the object being monitored can be traced in a one-dimensional manner, i.e., about an axis.
The induced voltage generated in detection coils 12A and 12B varies according to the displacement of optical detector element 8: thereby the detection of such voltage allows to detect the optical axis displacement angle .phi. of the detector element 8.
Also, by the arrangement in FIG. 35 as including a differential amplifier circuit, the optical axis displacement angle .phi. can be controlled in a precise manner.
In the above-describe Related art, the movable assembly can be typically small-sized and light-weight. No compensation for the dispersion of component parts is required.
RELATED ART 2
An "optical axis direction variable-type photo-detector" is shown in FIG. 36, compared with the Related art 1, a two-axis photo-detector is provided, having a pair of torsion bars perpendicular with each other.
In FIG. 36, the optical axis direction variable-type photo-detector 21, having the three layered construction, includes a silicon substrate 2 and a pair of upper and lower glass substrates 3, 4 bonded together. On each center of substrates 3 and 4, a pair of rectilinear recesses 3A, 3B are formed. The glass substrates 3, 4 each is bonded on the silicon substrate 2 in the manner that the upper glass substrate 3 is placed on the Si substrate 2 with the recess 3A on the lower side to be bonded thereon, while the lower glass substrate 4 is placed with the recess 4A on the upper side to be bonded on the Si substrate 2. As a result, a space is provided, in which the movable plate 5 having a detection element 8 thereon is allowed to rock therein.
In operation, a current flowed across the coil 7A causes the external movable plate 5A to rotate around the first torsion bars 6A, 6A according to the current direction, wherein the internal movable plate 5B also rotates integrally with the external movable plate 5A, and the photodiode 8 operates in the same manner as the case of the Related art 1.
The object to be Monitored can be traced in a two-dimensional manner.
RELATED ART 3
As shown in FIG. 37, 38 and 39, an optical axis direction variable-type photo-detector is provided. Different from the Related art 2, either of glass substrates 3, 4 is formed in a flat shape having no recesses 3A, 4A. Instead, a rectilinear opening 3a is formed in the movable plate 3 for allowing the detection light to directly enter the photodiode 8.
VARIATIONS
Other variations are possible for the optical detector element instead of a photodiode, such as a line sensor or an area sensor, each comprising a plurality of of photodiodes. Also, phototransitors, photo-conductors, or CCD may be employed. As necessary, microlens for converging the incident light is provided in front of the optical detector element.